a. Field of the Invention
This invention relates to a process for electrolytically coloring aluminum or any of its various alloys.
B. Prior Art
For electrolytic coloring of aluminum or aluminum alloys, there has been suggested and practiced extensively a process wherein workpieces are first anodized to form oxide films thereon and then electrolyzed in an electrolytic solution containing a metallic salt such as nickel salt by use of alternating or direct current. The workpieces are colored by deposition of the metal or metal oxide in the pores of the oxide films thereon.
Such a prior art process is generally poor in throwing power, so that particularly in the case of an irregularly shaped workpiece, its protuberant and recessed portions tend to be tinted noticeably differently. Furthermore, since a darker shade is usually produced on the end faces of workpieces, the counter electrode requires intricate masking.
It has also been proposed to make suitably combined use, in the electrolyzing operation of the above described prior art process, of alternating and direct currents or of other currents similar to or quite dissimilar from such currents in waveform. This practice has drawbacks in connection with the complexity of equipment required and its control.